In the formation of casts, it is useful to use a water hardenable material, such as Plaster of Paris or a water hardenable urethane, as disclosed for examples in U.S. Pat. No. 3,373,741 or in German Offenlegenschrift No. 2,651,089.
With regard to the construction of water hardenable casts, plaster of paris casts have been used for many years. They normally involve the use of several layers of cotton "skrim" or a very loosely woven cloth using thin threads and having large openings, and these layers of cloth are embedded in plaster of paris. In use, strips of the skrim and plaster of paris are dipped in water and wrapped around the injured portion of the anatomy. Normally padding is employed next to the skin to protect from the hardening cast material. As the plaster of paris hardens, it is somewhat exothermic, but there is no gas released. U.S. Pat. No. 3,043,298 (Brickman, et al.) assigned to Johnson & Johnson, discloses the addition of hydroxypropyl methyl-cellulose (HPMC) to a Plaster of Paris bandage to be used as an orthopaedic cast which gives the Plaster of Paris a creamy and viscous consistency or texture when wet with water just prior to application. More specifically, a plain Plaster of Paris cast without additives has a somewhat granular texture, akin to wet sand, while with the addition of HPMC it is somewhat smoother in texture with a consistency similar to mud or smooth clay.
Concerning water hardenable urethane casts, they are usually formed of a high strength fabric which may be 1/16 of an inch or so thick, and which is normally knitted so that there are small visible openings through the fabric. The water hardenable urethane material is impregnated into the fabric. At the time of use, assembly may be dipped in water prior to application to the injured part of the anatomy. Again, padding is usually employed to protect the skin from the cast material. In the case of urethane, the exothermic hardening reaction is accompanied by the release of carbon dioxide, and the wet urethane is very sticky. With the outgassing of the CO.sub.2 and the resulting bubbling out of the urethane material, the warm sticky assembly would be difficult for the doctor or orthopaedic technician to handle, and properly apply to the patient. One technique directed to overcoming this problem is disclosed in Mathew T. Scholz, et al. U.S. Pat. No. 4,667,660 and U.S. Pat. No. 4,774,937. As disclosed in these patents, the coefficient of friction of a curable resin sheet may be reduced by using either a lubricant of a certain type bound to the resin, and/or by using additive lubricants which are either (a) polysiloxanes, (b) surfactants, and polymers consisting of hydrophilic groups of certain types. It was the considered view of knowledgeable persons in the orthopaedic field that the techniques as described in the Scholz, et al. patents were the only practical way of obtaining the desired low coefficient of friction where water hardenable urethane materials were employed. Thus, for example, the assignee of the Brickman patent cited above, apparently employed the lubricants of the Scholz, et al. patents for its hardenable urethane cast assemblies, see Minnesota Mining and Manufacturing Co. v. Johnson & Johnson, 24 U.S.P.Q.2d 1321, 976 F.2d 1559 (CAFC 1992).
With regard to aspects of the invention emphasized in U.S. patent application Ser. No. 09/088,905 cited above, it has previously been proposed to use water-hardenable materials in orthopaedic supports and casts; and typical patents disclosing such products include U.S. Pat. No. 4,996,979, granted Mar. 5, 1991, and U.S. Pat. No. 4,683,877, granted Aug. 4, 1987. However, when materials as disclosed in these patents are employed, the flow of liquid through the open cell foam or layers of fabric, as well as the strength of the orthopaedic support may not be subject to the desired level of control.
It is also noted that these prior art products mentioned above have other problems. Thus, for example with regard to the casts or supports using layers of material, care must be taken to firmly engage the layers during the setting period to ensure unitary bonding of the entire layered cast or assembly. Doctors practicing in this area even have a saying: "rub it like you love it," to encourage full engagement of the layers during hardening of the water-hardenable material. This step obviously requires care and expertise, as it is undesirable to apply undue force to an injured limb involving broken bones, for example. Further, if this technique is not properly employed, the layers will not fully bond together, and the cast or support will be weak, and the layers could separate. Also with regard to the hardenable splints or supports using open cell foam, they may lack sufficient flexibility and conformability to properly fit the three-dimensional parts of the anatomy requiring splinting or support.
Flat rigid panels have also been proposed using doubleknit fabrics and hardenable resins, as indicated by U.S. Pat. No. 5,166,480, granted Nov. 24, 1992, and entitled "Knitted Fabric Panel Structure and Process of Manufacture." Attention is also directed to U.S. Pat. No. 5,334,442, granted Aug. 2, 1994. This patent discloses an intermediate pliant sheet which may be made of a single layer fabric such as a fiberglass fabric impregnated with a water-hardenable material. Then, on both sides of this pliant layer, the patentees disclose the use of layers of doubleknit material. Thus, with doubleknit material present in the assembly, it is not used to receive the water-hardenable material but is only used for padding.
As noted above, prior art orthopaedic products have involved shortcomings in the flow control of water to the water-hardenable material and the strength of the orthopaedic device.